This invention refers to a device for packaging products housed on a support with plastic film. Supports suitable for this type of packaging are the polystyrene trays sealed with transparent film, commonly used for packaging fruit, vegetables or other products. However, other types of supports are also utilizable, such as for example flat supports made of cardboard or other materials.
In the case of products which do not protrude from the container compartment, the container can be efficiently sealed quite easily with a relatively rigid and non-stretchable film, or sheet, secured to the edge of the compartment by various techniques, for example by sealing or rolling along the edge itself. Rigid film is easily handled for sealing over the tray.
On the contrary, whenever the products, due to their shape and size, protrude from the tray or in the case of products on a flat support, it is not possible to use a rigid sheet to seal the container. In this case it is necessary to use a very fine and consequently more difficult to handle stretchable film, which is tightly wrapped around the tray so as to cover the product to be packaged and peripherally have flaps folded underneath the tray, closely adhering. The folding of the flaps can be carried out either manually or mechanically.
It is obvious that, to ensure that the package is efficiently sealed, it is necessary to keep the peripheral flaps of the film quite long, resulting in an evident waste of material. Moreover, the integrity of the package cannot be guaranteed over time with absolute certainty; in fact, the adhesion of the film to the tray may diminish or the package may be inopportunely opened and then resealed. FR-A-1406789 discloses a packaging machine provided with a sealing head vertically movable over the product to be packaged so as to seal the film along the upper edge of the container. However, this kind of device involves a serious risk of breaking the film during the sealing operation. Further sealing machines are disclosed by US Pat. No. 3,378,991. The general scope of this invention is to obviate the above-mentioned problems by providing a device for packaging products in containers sealed with tightly stretched extensible plastic film, which makes it possible for the containers to remain sealed over time and to save a considerable quantity of film.
This scope is achieved according to the invention by providing a device for packaging products with an extensible plastic film on a base supporting the product, as claimed hereinafter. The innovative principles of this invention and its advantages with respect to the known technique will be more clearly evident from the following description of a possible exemplificative embodiment applying such principles, with reference to the accompanying drawings, in which: